I. Field
The present invention relates generally to data communication, and more specifically to techniques for adjusting power control using erasure detection in a wireless communication system.
II. Background
A wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations.
Multiple terminals may simultaneously transmit on the reverse link by multiplexing their transmissions to be orthogonal to one another. The multiplexing attempts to achieve orthogonality among the multiple reverse link transmissions in time, frequency, and/or code domain. Complete orthogonality, if achieved, results in the transmission from each terminal not interfering with the transmissions from other terminals at a receiving base station. However, complete orthogonality among the transmissions from different terminals is often not realized due to channel conditions, receiver imperfections, and so on. The loss in orthogonality results in each terminal causing some amounts of interference to other terminals. The performance of each terminal is then degraded by the interference from all other terminals.
On the reverse link, a power control mechanism may be used to control the transmit power of each terminal in order to ensure good performance for all terminals. This power control mechanism is normally implemented with two power control loops, which are often called an “inner” loop and an “outer” loop. The inner loop adjusts the transmit power of a terminal such that its received signal quality (SNR), as measured at a receiving base station, is maintained at a target SNR. The outer loop adjusts the target SNR to maintain a desired block error rate (BLER) or packet error rate (PER).
The conventional power control mechanism adjusts the transmit power of each terminal such that the desired block/packet error rate is achieved for the reverse link transmission from the terminal. An error detection code, such as a cyclic redundancy check (CRC) code, is typically used to determine whether each received data block/packet is decoded correctly or in error. The target SNR is then adjusted accordingly based on the result of the error detection decoding. However, an error detection code may not be used for some transmissions, e.g., if the overhead for the error detection code is deemed excessive. A conventional power control mechanism that relies on an error detection code cannot be used directly for these transmissions.
There is therefore a need in the art for techniques to properly adjust transmit power for a transmission when error detection coding is not used.